A generic filler neck is known from WO 2006/007618 A1. Because the hinge pin of the flap and the lock thereof are not fixed in space, the flap and the elements holding it can orient themselves in space in accordance with an oblique positioning of a filler tube with small diameter. It is thus no longer possible to circumvent the locking means.
Upon the insertion of a filler tube with the “correct” diameter, this rides on two cams facing towards one another of the elements, and the two elements are simultaneously forced outwards. However, it has been shown that the elements pivoted about a common pins are kinematically unfavorable, because the force in the longitudinal direction necessary to open the lock and the wear of the cams is very great.